Modeling the Magnetospheres of Jupiter and Saturn: Influences of the Internal Sources and of the Solar wind.

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The magnetospheres of Jupiter and Saturn, unlike the magnetosphere of the Earth, are characterized by strong internal plasma sources (Io for Jupiter and Enceladus for Saturn) and a fast rotation period. As a result, transport processes in both magnetospheres are very different from what is observed at Earth. Although of central interest, the combined effects of the solar wind and the internal sources on the magnetospheres of Jupiter and Saturn are still poorly understood. To study these influences, we will apply and improve a three-dimensional magnetohydrodynamic model, which we developed to describe the interactions between the solar wind and the magnetospheres of Jupiter and Saturn. With this model, we will study, among other things, the different magnetospheric current systems and their effects on the aurorae. We will also investigate the interesting differences between both magnetospheres due to the tilted dipole field of Jupiter and the nearly axisymmetric field of Saturn. Our model is particularly well suited for this task as it is currently the only one to treat the ionosphere-magnetosphere coupling through inclusion of collisions between neutrals and ions of the ionosphere. These collisions are crucial to obtain the proper response to changing internal sources and externally varying solar wind conditions. In a second phase, our model will also be adapted to study the magnetospheres of Uranus and Neptune. Our grand aim is to improve the general understanding of magnetospheric physics through comparative planetology of all four outer planets.